Open Emu is an open source project to bring game emulation to OS X as a first class citizen, leveraging modern OS X technologies such as Cocoa, Core Animation and Quartz, and 3rd party libraries like Sparkle for auto-updating. Open Emu is based on a modular architecture, allowing for game-engine plugins, this means Open Emu can support a host of different emulation engines and back-ends while retaining a familiar OS X native front-end. (text from their website: https://github.com/OpenEmu/OpenEmu).

Soon, CrocoDS, the greatest Amstrad emulator (yes, I know…), will be available for Open Emu.